Mother's Day seems to see us get close to the peak of autumn-colouring leaves in Sydney. Around this time last year, I wrote a blog about some of the deciduous trees that grow well in our climate, such as the Chinese Tallow tree (Sapium sebiferum)*, the Chinese pistachio tree (Pistacia chinensis), crepe myrtle (Lagerstroemia indica) and the basic Japanese maple (Acer palmatum). I didn't include a number of trees, because they either get too big or only grow well in the more elevated suburbs with richer, cooler soil than many of us have.
This is not to say that gardeners in other suburbs should not attempt to grow these trees if they have a deep desire to try them. Sometimes a cool microclimate, protected from hot afternoon sun in summer, with good, rich, moist soil can be found in a warmer garden which allows triumph with some of these specimens.
Probably the most stunning autumn foliage in this category belongs to the tupelo (Nyssa sylvatica), a conical-shaped tree to around 15m tall, with branches held in distinct horizontal layers. It is one of the first trees to colour in mid-late April, when its shiny leaves metamorphose to mainly brilliant crimson with orange and yellow touches, or a rich mixture of all three colours, glowing like fire when backlit by the sun. This tree needs moist, rich soil to flourish.
The broad, oval leaves of the golden elm (Ulmus glabra 'Lutescens', ht 7-10m) gradually change from lime-green to clear yellow from late summer onwards. This tree is vase shaped when young but assumes a wider, round-headed shape with age. This tree seems prone to borer attack in Sydney, so a watchful eye needs to be kept out for the telltale sawdust of this pest. It is prone to leaf-scorch if subject to hot afternoon sun in summer, so should probably be given a slightly protected position.
The ash trees have fine fingers of foliage, with the golden ash (Fraxinus excelsior 'Jaspidea', syn. 'Aurea', ht 10-12m) turning to glittering pale gold, whilst the claret ash (Fraxinus angustifolia 'Raywood', ht 15-20m) becomes a deep wine red. The golden elm and the ash trees need good soil and a well-drained position, and are worth trying although they are probably seen at their best in the cooler elevated areas of Sydney. The ash trees, particularly the claret ash, seem to be prone to die-back in Sydney, often after periods of very heavy rain, underlining their need for well-drained soil.
The dogwood (Cornus florida, ht 6m) will be more likely to produce good autumn tints in cooler suburbs and is more liable to flower well there in spring too, although on the whole it is not at its happiest in Sydney. The beautiful silver birch (Betula pendula, ht 12-15m) is also more prone to survive and show its butter yellow autumn leaves in these cooler areas, as long as it can be assured of good drainage and a cool root run, as it is vulnerable to death by root rot.
There are some true giants amongst the autumn foliage trees seen in Sydney. It is probably not wise to actually plant any of these in one's own garden, but some of us inherit one of them when we acquire an older garden, and many can be observed in many street plantings. Because it colours so well throughout Sydney, one of the most ubiquitous is the liquidambar tree (Liquidambar styraciflua) which can grow to 20-30 m with wide spreading branches sweeping low to the ground. These trees can display a brilliant patchwork of citrus yellow, copper, scarlet and deep purple palmate leaves even in our mild climate, and provide an awe-inspiring sight in autumn. Their huge, greedy root systems can cause problems with pipes and house foundations, as well as making it impossible to grow other plants anywhere in their vicinity. All is forgiven, however, when the tree assumes its vivid autumnal mantle. The angst sets in again when one (or one's husband) has to deal with the mountains of fallen leaves.
There are few deciduous conifer trees in the world, but some can be seen around Sydney. The gingko tree (Gingko biloba) is one of them, an ancient and very unusual deciduous conifer tree, with beautiful fan-shaped leaves which are remarkably like big maidenhair fern leaves, turning translucent butter-yellow in autumn. Capable of reaching a height up to 25m tall in cold climates, it probably will not reach that size here but will still form a substantial-sized tree; the erect cultivar 'Fastigiata' grows no more than 10-12m tall. The maidenhair tree does grow reasonably well in Sydney, especially in the cooler elevated suburbs. Male trees are to be preferred, as the female plants produce unpleasantly scented fruit.
Another deciduous conifer is the swamp cypress (Taxodium distichum), a beautiful cone-shaped tree growing to 20-24 m, with tiny feathery leaves turning a foxy-brown colour in autumn. Back-lit by the sun, this tree can have an unearthly tawny glow, but like all the other big trees mentioned here, it is probably best admired from afar. The noble dawn redwood (Metasequoia glyptostroboides) has a similar shape, and develops gold and russet foliage autumn. This tree has the potential to grow to 60 m tall!
A trip to the Mt Tomah Botanic Garden at this time of year will reveal many of these trees in all their autumn splendour.
* The Chinese tallowwood is now called Triadica sebifera. In many areas, especially warm zones, it is now classed as a noxious weed because it spreads by seed and suckers, and can invade bushland.
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